1. Field of the Invention
The present invention relates to a vibration motor having an improved support structure between a rotor for generating eccentric rotation and a stator for supporting rotation of the rotor.
2. Description of the Related Art
A communication device generally uses a bell and vibrator to notify a user of call incoming. In a vibration mode, generally a small-sized vibration motor is actuated transferring driving force to a housing of the communication device to vibrate the communication device.
The vibration motor currently applied to a mobile telephone is discriminated into a flat type vibration motor and a cylinder type vibration motor. The flat type vibration motor has a relatively simple vibration structure, e.g., for rotating a weight which is placed inside the motor. The flat type vibration can be fabricated thin so that components of a mobile phone can be miniaturized. Owing to these advantages, application of the flat type vibration motor is gradually spreading.
FIG. 1 is a sectional view of a conventional flat type vibration motor. The conventional flat type vibration motor comprises a stator (i.e., stator assembly) as a stationary member and a rotor (i.e., rotor assembly) as a rotary member. That is, a lower board 101 is bonded to an upper face of a circular flat bracket 100, and an annular magnet 102 is attached concentrically to an upper face of the lower board 101 in an equal fashion.
The bracket 100 is covered from above with a housing 110, and the bracket 100 and the housing 110 are connected by a central shaft 105. The shaft 105 has a rotor 120, as shown in FIG. 2, which includes a bearing 121, an upper board 122, a commutator 123, winding coils 124, a weight 125 and an insulator 126.
The upper board 122 is a circular printed circuit board, and when powered from the commutator 123 which is attached to the underside of the upper board 122, supplies different electric power to each of the winding coils 124 through a pattern formed in the top and the underside thereof. The commutator 123 has a number of segments which are buried in the underside of the upper board 122 around the center of rotation at a predetermined interval, exposing contact faces thereof. The winding coils 124 are arranged flush with each other on a common radius and opposed to the magnet 102 placed under the winding coils 124. One of the winding coils 124 is supplied with electric power having a polarity different from that of the other one of the winding coils 124.
The weight 125 is generally made of high specific gravity material such as tungsten (W), and attached to the upper board 122 in a position opposite to the winding coils 124 on the upper board 122 to determine the eccentricity of the motor. The insulator 126 is a component for ensuring secure mutual attachment among the bearing 121, the winding coils 124 and the weight 125 on the upper board 122 as well as and imparting insulation to the same. At this time, the stator and the rotor 120 are electrically connected to each other by a pair of brushes 127, which have their lower ends fixed to the lower board 101 and their upper ends in slidable contact with the commutator 123.
The above vibration motor is referred to as a brush type vibration motor which has drawbacks that the brush 127 causes mechanical abrasion or generates electric sparks while passing through the interval of the segments during rotation of the rotor. This situation causes byproducts functioning as a major factor of damaging the stability of electric contacts, which in turn may generate noises or degrade the performance of the vibration motor. Then, the lifetime of the vibration motor may be also shortened.
In order to overcome drawbacks of the brush type vibration motor as above, there is currently being studied a brushless vibration motor which does not have the brush or the commutator. The brushless vibration motor is so designed that an Integrated Circuit (IC) chip is employed for actuation of the motor and a magnet is placed in a rotor unlike the existing brush type motor.
FIG. 3 is a sectional view of a conventional brushless vibration motor. In FIG. 3, a rotor includes a yoke 202, a magnet 203 mounted on the underside of the yoke 202 and a weight 205 mounted on one end of the yoke 202. A central portion of the yoke 202 is fixedly coupled with a rotary shaft 204 so that the rotary shaft 204 projects downward.
In FIG. 3, the stator includes a bearing 208 which supports rotation of the rotary shaft 204 while contacting the rotary shaft 204 of the rotor. The bearing 208 is inserted into a projected portion which is formed in a central portion of an underlying bracket 209, and a board 206 is placed on the bracket 209. A coil 210 is attached on the board 206, and an IC chip 211 placed on the board 206 supplies AC power to the coil 210.
The conventional brushless vibration motor is so designed that the rotary shaft 204 is fixed to the rotor. Then, during operation of the vibration motor, the rotor vertically moves to collide against a housing 201 and the bracket 209, making loud noises as well as having bad effect to the lifetime of the housing and the bracket.
Furthermore, the rotor of the brushless vibration motor has a mass larger than that of the rotor of the conventional brush type vibration motor. When the rotary shaft is coupled with the rotor like the brush type vibration motor, load is concentrated to the bracket thereby degrading the reliability of the bracket.
The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to provide a vibration motor which comprises a bearing coupled with a rotor and a stationary shaft supported by a stator in order to ensure rotation of the rotor more stable, reduce noises and guarantee reliability.
It is another object of the invention to provide a vibration motor which has an improved structure of a bearing of a rotor and a washer for supporting the bearing in order to sufficiently endure the axial load of the rotor and thus elevate rotation rate while reducing power consumption.
According to an aspect of the invention for realizing the above objects, there is provided a vibration motor comprising: a rotor having an eccentric mass; a stator for supporting rotation of the rotor; a stationary shaft inserted into a rotation center of the rotor and having upper and lower ends supported by the stator; a bearing having upper and lower ends smaller in cross sectional area than a central portion of the bearing, and coupled with the rotor at the rotation center thereof to contact an outer periphery of the stationary shaft; a first washer mounted on an inner and upper central portion of the stator for elastically supporting the stationary shaft, and being in contact with an upper face of the stationary shaft; and a second washer being in contact with a lower end of the bearing and mounted on the stator around the stationary shaft to support the rotor.
Preferably, the rotor includes a coil and a commutator having a plurality of segments for alternating electric power to the coil, and wherein the stator includes a magnet mounted in a position corresponding to the position of the coil of the rotor and a brush contacting the commutator for applying electric power. Also preferably, the stator includes a coil and an Integrated Circuit (IC) chip for alternating electric power to the coil, and wherein the rotor includes a magnet.
Preferably, the stator has a recess formed in an inner and upper central portion thereof, and the first washer is positioned to cover the recess. Also preferably, the stator has a projected column in an inner and lower central portion thereof for receiving the stationary shaft, and wherein the second washer is placed on a top of the projected column.
Preferably also, the projected column is coupled with a bush for applying clamping force, and the second washer is placed on a top of the bush.
Also preferably, the first and second washers have an outside diameter larger than that of the bearing, the bearing has tapered upper and lower ends, or the bearing has rounded edges in upper and lower ends.
According to another aspect of the invention for realizing the above objects, there is provided a vibration motor comprising: a magnetic bracket mounted with a coil and an Integrated Circuit (IC) chip for supplying AC power to the coil, the bracket having a projected column formed with a through hole in a central portion of the projected column; a housing for covering the bracket, the housing having an internal space and a recess formed in an upper central portion of the housing; a stationary shaft having a first end portion inserted into the projected column and a second end portion inserted into the recess; a yoke having at least one magnet mounted on an underside of the yoke, the magnet being magnetized into a plurality of poles, and a weight for introducing eccentric mass attached to the yoke; a bearing having upper and lower ends smaller in cross sectional area than a central portion of the bearing, and coupled with the rotor at the rotation center thereof to contact an outer periphery of the stationary shaft; a first washer arranged in the recess for elastically supporting the stationary shaft, and being in contact with an upper face of the stationary shaft; and a second washer being in contact with a lower end of the bearing and mounted on the stator around the stationary shaft to support the rotor.
Preferably, the coil and the IC chip for supplying AC power to the coil are provided on an inner lower face of the housing, and the first and second washers have an outer diameter smaller than that of the bearing.
Also preferably, the bearing has tapered upper and lower ends, or rounded edges formed in upper and lower ends. Preferably, the projected column is coupled with a bush for applying clamping force, and the second washer is placed on a top of the bush.
The vibration motor of the invention includes a contact structure having the stationary shaft arranged in a contact portion in the side of the stator, in which the rotor rotates in contact with the stator, and the bearing coupled in the side of the rotor. In addition, the vibration motor may further include a structure which enables the washer in the side of the rotor and the washer for supporting the bearing to contact each other at a small area. The vibration motor having the shaft structure of the invention is preferably a brushless vibration motor, but not limited thereto. On the contrary, the vibration motor of the invention may include a brush.
The brushless motor has semi-permanent lifetime since it to the letter does not have a brush or a commutator used in a DC motor. In comparison to the DC motor, the brushless motor comprises the rotor having the permanent magnet and the stator having the coils. The brushless motor further comprises a sensor for detecting the rotation angle of the rotor since it is required to regulate flow of electric power supplied to the coils according to the rotation angle of the rotor.